This invention relates to plasma etching methods.
Integrated circuitry density continues to increase and feature dimensions continue to get smaller. One aspect of semiconductor integrated circuitry fabrication is the etching of contact openings through insulating layers, such as borophosphosilicate glass (BPSG), to expose inward circuit regions to which electrical connection is desired.
Contact openings are typically presently formed by depositing an organic masking layer (photoresist, being one example) outwardly of the layer within which the opening is to be formed. The masking layer is patterned to leave desired contact openings therethrough while leaving other areas of the layer covered (i.e., masked) such that etching will not there occur. The insulating layer is thereafter etched through the organic masking layer openings, preferably highly selectively to remove the insulating layer at a substantially greater rate than any etching of the masking layer. The ultimate goal is to outwardly expose a desired region of the underlying substrate.
Forming such openings is preferably conducted using a highly anisotropic etch, such as a plasma etch. One such prior art etch employs an Applied Materials IPS Dielectric Etcher using reactive gas flows of CHF3 and CHF3 at a volumetric ratio of 11:9, respectively. It was discovered using such chemistry that as the minimum feature dimension of the contact opening fell to 0.3 micron and below. the etched sidewalls of the feature layer being etched were becoming striated or otherwise roughened to a degree sufficient to impact critical dimension (CD) of the feature and overall yield. Such roughening apparently resulted from formation of striations or other roughenings in the opening sidewalls of the photoresist, which were being mask transferred to the feature layer. Such roughening was more prone to occur in useful processing windows in high density deposition tools, namely in processing windows where acceptable uniformity across the substrate could be achieved. Such sidewall striations might also have occurred in etching of larger contact openings, but were not problematic due to the larger opening dimensions. However at the 0.3 micron level and below, roughened or otherwise striated sidewalls within a feature opening (i.e., a damascene trough, a contact opening or other feature) can adversely affect CD and yield.
The invention was motivated in addressing and overcoming this particular problem, yet is not so limited. Aspects of the invention are seen to have applicability to other aspects of plasma etching, with the invention only being limited by the accompanying claims, appropriately interpreted in accordance with the Doctrine of Equivalents.
The invention comprises plasma etching methods. In one implementation, a patterned organic masking layer is formed outwardly of a feature layer to be etched. The patterned organic masking layer has at least one feature pattern having a minimum feature dimension of less than or equal to 0.3 micron. The feature layer has a thickness inwardly of the one feature pattern which is to be etched to form the one feature pattern in the feature layer. The at least one feature pattern is plasma etched into the feature layer using the organic masking layer as a mask. The plasma etching comprises at least one etching segment where at least 30% of said thickness of the feature layer is etched using an etching gas comprising one gas compound comprising carbon, hydrogen and at least one halogen present in the etching gas at greater than or equal to 70% concentration by volume as compared to all carbon, hydrogen and halogen containing gas compounds in the etching gas. Such plasma etching is conducted under conditions effective to produce at least that portion of the one feature pattern in the feature layer formed during the one etching segment to have a sidewall taper of less than or equal to 5xc2x0 and an organic masking layer top outer surface roughness proximate the feature pattern at a conclusion of the etching segment which is characterizable by an average value less than 100 Angstroms. Such average value is determinable by scanning electron microscopy as an average maximum size of all surface discernible objects of the patterned masking layer as measured and averaged along any 0.3 micron length of top outer surface from the one feature pattern.
Other implementations are also contemplated.